Atrial fibrillation is the most common heart arrhythmia in the world, affecting over 2.5 million people in the United States alone. In fibrillation the upper chambers of the heart, known as the atria, quiver rapidly instead of beating in a steady rhythm. The rapid quivering reduces the heart's ability to properly function as a pump.
The disorder typically increases the risk of acquiring a number of potentially deadly complications, including thrombo-embolic stroke, dilated cardiomyopathy, and congestive heart failure. Quality of life is also impaired by atrial fibrillation symptoms such as palpitations, chest pain, dyspnea, fatigue, and dizziness. People with atrial fibrillation have, on average, a five-fold increase in morbidity and a two-fold increase in mortality compared to people with normal sinus rhythm.
Treatments for atrial fibrillation include drug therapy, electrocardioversion, and surgical or intravascular ablation techniques. Surgical ablation is an invasive procedure whereby the surgeon creates a maze-like pattern of incisions on the inside of the patient's atria. The scarring that results acts to block the abnormal electrical pathways in the heart that lead to atrial fibrillation. Surgical ablation has a much higher success rate than drug therapies and lacks the potential for side effects presented by drug treatment. However, highly invasive (e.g., open-chest) procedures can present substantial risks.
Intravascular ablation similarly creates scar tissue that impedes the travel of errant electrical impulses in the heart tissue. Radio frequency and microwaves are exemplary energy sources for such ablation. Additionally, cryoablation techniques have also been explored.
One benefit of radio frequency, microwave, and cryoablation is the ability to deliver therapy via a catheter. These ablation techniques use a less invasive, transvenous approach. To perform such a procedure, specifically a cryoablation procedure, the tip of a cryoablation catheter is typically inserted into and advanced within the vasculature of a patient until the tip is located adjacent to the targeted tissue. Next, in a typical cryocatheter, a refrigerant is pumped into the catheter for expansion into an expansion chamber that is located at or near the catheter tip. The expansion of the refrigerant cools the catheter tip and target tissue. By cooling the tip of a cryoablation catheter to sub-zero temperatures, the cells in the heart responsible for conducting the arrhythmia are altered so that they no longer conduct electrical impulses. However, in some instances, the refrigerant is not evenly distributed within the desired region of the expansion chamber. This results in the non-uniform or uneven ablation of the targeted tissue.
Accordingly, current treatments for atrial fibrillation could benefit from improved techniques and devices for cyroablating the cells in the heart responsible for conducting cardiac arrhythmias.